with such a similar AA%, you wouldn't need to in this case. but the way to convert is multiply the AA% and weight for the recipe. 1 x 9.6 = 9.6. then divide that by the AA% of your hops, 9.6/9.3 = 1.03. so you'd need 1.03 oz of 9.3% cascades to = 1 oz of 9.6% cascades.
say you have a recipe that calls for 1 oz of 9.3% amarillo, but you have 10.4% amarillo, using the same math, you'd need .89 oz of the 10.4% amarillo for that recipe.

Please note that you SHOULD NOT adjust a recipe's flavor or aroma additions based on a different AA%. AA% is useful only for bittering. The flavors and aromas come from other compounds. So if your recipe calls for 1 oz of Cacades at 10 minutes, throw in 1 oz of Cascades at 10 minutes, regardless of the AA%. Of course this means you may need to readjust your bittering addition to keep the total IBUs the same, beyond your original adjustment for AA%.

At what point in the boil are the additions considered flavoring hops? With a 1.8-2% AAU difference between what I have ad what the recipe calls for, should I STILL not adjust my flavoring weights?

Correct. If you're adding hops at 15 minutes, those are your flavoring hops. Adding more to adjust the IBUs means that you'd add more (or less) hops. The flavor is a complex thing, and IBUs really don't matter much as compared to the flavor you're getting.

I'd say any hops added at 20 minutes or less shouldn't be adjusted for AAUs, as they are for flavoring and aroma.

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